Identification of normalized and reconstituted milk by the methods of digital colorimetry and IR spectroscopy

A rapid and easy to use method for identification and differentiation of normalized and reconstituted milk using digital colorimetry and near-infrared spectroscopy is proposed. A box device with LEDs (λ = 365, 390, 850, 880 nm) built in through resistors with a light scattering angle of 20° was used. A smartphone with PhotoMetrix PRO ® , ColorGrab, RGBer applications and an IR-Fourier spectrometer for a near-IR region (4000 – 10,000 cm –1 ) were taken to record the analytical signal. Applications TQ Analyst, The Unscrambler X, XLSTAT, were used for processing the obtained diffuse reflectance spectra and colorimetric parameters. The principal component analysis ( PCA ) and hierarchical cluster analysis ( HCA ) were used to identify and differentiate the analyzed milk samples. The determination of the mass fraction of fat and protein in dairy products was carried out using the partial least squares (PLS) regression algorithm. The points corresponding to normalized and reconstituted milk are located in different quadrants on PCA plots in methods of digital colorimetry and IR spectroscopy. Using PCA and HCA graphs, it appeared possible to distinguish the analyzed milk by the type and differentiate skim milk by the protein content. The possibility of determining the fat and protein content in the studied milk samples using chemometric methods of analysis has been demonstrated. The relative standard deviation of the analysis results did not exceed 0.03 for reconstituted and normalized milk, and for skim milk — 0.02.